Fishery

Fishery is a library for setting up JavaScript objects for use in tests and anywhere else you need to set up data. It is loosely modeled after the Ruby gem, factory_bot.

Fishery is built with TypeScript in mind. Factories accept typed parameters and return typed objects, so you can be confident that the data used in your tests is valid. If you aren't using TypeScript, that's fine too – Fishery still works, just without the extra typechecking that comes with TypeScript.

Installation

Install fishery with:

npm install --save-dev fishery

or

yarn add --dev fishery

Usage

A factory is just a function that returns your object. Fishery provides several arguments to your factory function to help with common situations. After defining your factory, you can then call build() on it to build your objects. Here's how it's done:

Define and use factories

1// factories/user.ts
2import { Factory } from 'fishery';
3import { User } from '../my-types';
4import postFactory from './post';
5
6const userFactory = Factory.define<User>(({ sequence }) => ({
7  id: sequence,
8  name: 'Rosa',
9  address: { city: 'Austin', state: 'TX', country: 'USA' },
10  posts: postFactory.buildList(2),
11}));
12
13const user = userFactory.build({
14  name: 'Susan',
15  address: { city: 'El Paso' },
16});
17
18user.name; // Susan
19user.address.city; // El Paso
20user.address.state; // TX (from factory)

Asynchronously create objects with your factories

In some cases, you might want to perform an asynchronous operation when building objects, such as saving an object to the database. This can be done by calling create instead of build. First, define an onCreate for your factory that specifies the behavior of create, then create objects with create in the same way you do with build:

1const userFactory = Factory.define<User>(({ onCreate }) => {
2  onCreate(user => User.create(user));
3
4  return {
5    ...
6  };
7});
8
9const user = await userFactory.create({ name: 'Maria' });
10user.name; // Maria

create returns a promise instead of the object itself but otherwise has the same API as build. The action that occurs when calling create is specified by defining an onCreate method on your factory as described below.

create can also return a different type from build. This type can be specified when defining your factory:

Factory.define<ReturnTypeOfBuild, TransientParamsType, ReturnTypeOfCreate>

Documentation

Typechecking

Factories are fully typed, both when defining your factories and when using them to build objects, so you can be confident the data you are working with is correct.

1const user = userFactory.build();
2user.foo; // type error! Property 'foo' does not exist on type 'User'

1const user = userFactory.build({ foo: 'bar' }); // type error! Argument of type '{ foo: string; }' is not assignable to parameter of type 'Partial<User>'.

1const userFactory = Factory.define<User, UserTransientParams>(
2  ({
3    sequence,
4    params,
5    transientParams,
6    associations,
7    afterBuild,
8    onCreate,
9  }) => {
10    params.firstName; // Property 'firstName' does not exist on type 'DeepPartial<User>
11    transientParams.foo; // Property 'foo' does not exist on type 'Partial<UserTransientParams>'
12    associations.bar; // Property 'bar' does not exist on type 'Partial<User>'
13
14    afterBuild(user => {
15      user.foo; // Property 'foo' does not exist on type 'User'
16    });
17
18    return {
19      id: `user-${sequence}`,
20      name: 'Bob',
21      post: null,
22    };
23  },
24);

build API

build supports a second argument with the following keys:

• transient: data for use in your factory that doesn't get overlaid onto your result object. More on this in the Transient Params section
• associations: often not required but can be useful in order to short-circuit creating associations. More on this in the Associations section

Use params to access passed in properties

The parameters passed in to build are automatically overlaid on top of the default properties defined by your factory, so it is often not necessary to explicitly access the params in your factory. This can, however, be useful, for example, if your factory uses the params to compute other properties:

1const userFactory = Factory.define<User>(({ params }) => {
2  const { name = 'Bob Smith' } = params;
3  const email = params.email || `${kebabCase(name)}@example.com`;
4
5  return {
6    name,
7    email,
8    posts: [],
9  };
10});

Params that don't map to the result object (transient params)

Factories can accept parameters that are not part of the resulting object. We call these transient params. When building an object, pass any transient params in the second argument:

1const user = factories.user.build({}, { transient: { registered: true } });

Transient params are passed in to your factory and can then be used however you like:

1type User = {
2  name: string;
3  posts: Post[];
4  memberId: string | null;
5  permissions: { canPost: boolean };
6};
7
8type UserTransientParams = {
9  registered: boolean;
10  numPosts: number;
11};
12
13const userFactory = Factory.define<User, UserTransientParams>(
14  ({ transientParams, sequence }) => {
15    const { registered, numPosts = 1 } = transientParams;
16
17    const user = {
18      name: 'Susan Velasquez',
19      posts: postFactory.buildList(numPosts),
20      memberId: registered ? `member-${sequence}` : null,
21      permissions: {
22        canPost: registered,
23      },
24    };
25
26    return user;
27  },
28);

In the example above, we also created a type called UserTransientParams and passed it as the second generic type to define. This gives you type checking of transient params, both in the factory and when calling build.

When constructing objects, any regular params you pass to build take precedence over the transient params:

1const user = userFactory.build(
2  { memberId: '1' },
3  { transient: { registered: true } },
4);
5
6user.memberId; // '1'
7user.permissions.canPost; // true

Passing transient params to build can be a bit verbose. It is often a good idea to consider creating a reusable builder method instead of or in addition to your transient params to make building objects simpler.

After-build hook

You can instruct factories to execute some code after an object is built. This can be useful if a reference to the object is needed, like when setting up relationships:

1const userFactory = Factory.define<User>(({ sequence, afterBuild }) => {
2  afterBuild(user => {
3    const post = factories.post.build({}, { associations: { author: user } });
4    user.posts.push(post);
5  });
6
7  return {
8    id: sequence,
9    name: 'Bob',
10    posts: [],
11  };
12});

After-create hook

Similar to onCreate, afterCreates can also be defined. These are executed after the onCreate, and multiple can be defined for a given factory.

1const userFactory = Factory.define<User, {}, SavedUser>(
2  ({ sequence, onCreate, afterCreate }) => {
3    onCreate(user => apiService.create(user));
4    afterCreate(savedUser => doMoreStuff(savedUser));
5
6    return {
7      id: sequence,
8      name: 'Bob',
9      posts: [],
10    };
11  },
12);
13
14// can define additional afterCreates
15const savedUser = userFactory
16  .afterCreate(async savedUser => savedUser)
17  .create();

Extending factories

Factories can be extended using the extension methods: params, transient, associations, afterBuild, afterCreate and onCreate. These set default attributes that get passed to the factory on build. They return a new factory and do not modify the factory they are called on :

1const userFactory = Factory.define<User>(() => ({
2  admin: false,
3}));
4
5const adminFactory = userFactory.params({ admin: true });
6adminFactory.build().admin; // true
7userFactory.build().admin; // false

params, associations, and transient behave in the same way as the arguments to build. The following are equivalent:

1const user = userFactory
2  .params({ admin: true })
3  .associations({ post: postFactory.build() })
4  .transient({ name: 'Jared' })
5  .build();
6
7const user2 = userFactory.build(
8  { admin: true },
9  {
10    associations: { post: postFactory.build() },
11    transient: { name: 'Jared' },
12  },
13);

Additionally, the following extension methods are available:

• afterBuild - executed after an object is built. Multiple can be defined
• onCreate - defines or replaces the behavior of create(). Must be defined prior to calling create(). Only one can be defined.
• afterCreate - called after onCreate() before the object is returned from create(). Multiple can be defined

These extension methods can be called multiple times to continue extending factories:

1const sallyFactory = userFactory
2  .params({ admin: true })
3  .params({ name: 'Sally' })
4  .afterBuild(user => console.log('hello'))
5  .afterBuild(user => console.log('there'));
6
7const user = sallyFactory.build();
8// log: hello
9// log: there
10user.name; // Sally
11user.admin; // true
12
13const user2 = sallyFactory.build({ admin: false });
14user.name; // Sally
15user2.admin; // false

Adding reusable builders (traits) to factories

If you find yourself frequently building objects with a certain set of properties, it might be time to either extend the factory or create a reusable builder method.

Factories are just classes, so adding reusable builder methods can be achieved by subclassing Factory and defining any desired methods:

1class UserFactory extends Factory<User, UserTransientParams> {
2  admin(adminId?: string) {
3    return this.params({
4      admin: true,
5      adminId: adminId || `admin-${this.sequence()}`,
6    });
7  }
8
9  registered() {
10    return this
11      .params({ memberId: this.sequence() })
12      .transient({ registered: true })
13      .associations({ profile: profileFactory.build() })
14      .afterBuild(user => console.log(user))
15  }
16}
17
18// instead of Factory.define<User>
19const userFactory = UserFactory.define(() => ({ ... }))
20
21const user = userFactory.admin().registered().build()

To learn more about the factory builder methods params, transient, associations, afterBuild, onCreate, and afterCreate, see Extending factories, above.

Advanced

Associations

Factories can import and reference other factories for associations:

1import userFactory from './user';
2
3const postFactory = Factory.define<Post>(() => ({
4  title: 'My Blog Post',
5  author: userFactory.build(),
6}));

If you'd like to be able to pass in an association when building your object and short-circuit the call to yourFactory.build(), use the associations variable provided to your factory:

1const postFactory = Factory.define<Post>(({ associations }) => ({
2  title: 'My Blog Post',
3  author: associations.author || userFactory.build(),
4}));

Then build your object like this:

1const jordan = userFactory.build({ name: 'Jordan' });
2factories.post.build({}, { associations: { author: jordan } });

If two factories reference each other, they can usually import each other without issues, but TypeScript might require you to explicitly type your factory before exporting so it can determine the type before the circular references resolve:

1// the extra Factory<Post> typing can be necessary with circular imports
2const postFactory: Factory<Post> = Factory.define<Post>(() => ({ ...}));
3export default postFactory;

Rewind Sequence

A factory's sequence can be rewound with rewindSequence(). This sets the sequence back to its original starting value.

Contributing

See the CONTRIBUTING document. Thank you, contributors!

Credits

This project name was inspired by Patrick Rothfuss' Kingkiller Chronicles books. In the books, the artificery, or workshop, is called the Fishery for short. The Fishery is where things are built.

License

Fishery is Copyright © 2021 Stephen Hanson and thoughtbot. It is free software, and may be redistributed under the terms specified in the LICENSE file.

About thoughtbot

This repo is maintained and funded by thoughtbot, inc. The names and logos for thoughtbot are trademarks of thoughtbot, inc.

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